Originally posted by OvidiuRoSb I don't know if this is the reason, but make sure you disabled the SR from body.
For using the stabilization from the lens, SR from body must be disabled.
Well, I had another look at it, since I hadn't tried it for more than a year, and found it is possible to use it after all!
The behaviour I remember when I got the Sigma 70-200 for my K-3, was that the lenses optical stabilization (OS) would be active in photo mode and also in Video mode up until pressing record. Now I find that its only enabled when focusing (either by half press or back button focusing). The OS loses power about 1 second after releasing the focus button. I guess that makes sense from a power saving perspective. So either I really stuffed up my initial testing or there has been change in one of the firmware versions along the way.
So now I can get effective OS by keeping focus active during recording. For video, I can ensure actual focusing doesn't get stuffed up (by the cameras rather clumsy video focusing) by switching the AF switch on the lens to Off and holding the back AF button down all the time. Unfortunately, it's not so convenient for stills mode anymore.
No idea if this handling of in lens OS applies to the K-1 though.
John.